Chapter 12 Flashcards
What percentage of the Sun’s mass must a star be to be able to fuse hydrogen?
Must be at least 8% of the Sun’s mass (or 80 times Jupiter’s mas)
What are stars below to mass of 8% of the Sun’s mass called?
Brown dwarfs
What are the two properties on which we can base the differentiation between small star and large gas planets?
Either their formation or mass
What are two reasons why exoplanets are impossible to see with current technology?
They are too dim and they orbit too close to their parent stars
What is the detection method astrometry?
Measuring the wobble induced in the plane-of-sky motion of the star by the planets by observing its position over time
What is the main difficulty with the detection method astrometry?
Our current technology is not accurate enough to detect wobbles at far distances
What is the detection method pulsar planets?
Planets being found orbiting pulsars, by detecting the changes is the very regular pulses
What is the detection method transit?
Planets observed at inclinations near 90 degrees will pass in front of host stars, dimming their light
What is an observational challenge with the detection method transits?
The volume of sample, and time it takes for each transit, means tedious to preform
As of 2015, how many potential exoplanets had been found and how many of those have been confirmed by Kepler telescope?
4202 potential planets and 1002 confirmed
What is the detection method microlensing?
A planet can actually produce a brightening (rather than dimming) of a background star by bending the light with its gravity well
How many detection of small planets far from their star have their been from mircolensing?
34 detections so far
What is the detection method radial velocity?
The planet’s gravity pulls its hosts star back and forth in its orbit causing the light to be blueshifted and redshifted
What was the first star discovered around a sun-like star and what method was used?
51 Pegasi B was discovered using radial velocity method
Why is 51 Pegasi B the prototypical “hot Jupiter”?
It has a greater radius, but lower mass that Jupiter, and orbits extremely close to its parent star and is therefore super heated to 700 K
What are some observational challenges associated with detection method radial velocity
Required high-precision repeatable spectroscopic measurements of Doppler shifts to approx 1 m/s accuracy
To what kind of exoplanets is the detection method radial velocity most sensitive?
Massive planets that orbit near their stars
What is the detection method direct detection?
There are two ways to directly detect the light from planets; 1. remove the starlight before imaging, 2. remove after (using models of stellar evolution)
What method is used to directly image exoplanets?
Adaptive optics
What is a coronagraph?
The method used to cover starlight will direct imaging exoplanets
What is Metallicity?
The abundance of element heavier than He relative to the Sun
Why is it that many more large exoplanets have been found compared to small exoplanets?
Solely because large planets are easier to detect
What is the outstanding problem in the study of exoplanets?
The fact that we find so many large exoplanets orbiting so close to their stars contradicts our understanding of the formation of our on SS
Why have we found so many exoplanets orbiting very close to their stars?
Because we have only been surveying since 1988 (ex. Saturn takes 30yrs to orbit and therefore would have been detected yet)
What are the 4 components an exoplanet must have in order to be considered “Earth-like”
- moderate temperature, 2. liquid water, 3. organic molecules, 4. energy available
What is the habitable zone?
The “appropriate region” (can simply and vaguely defined as “where water can exist”)
Is the habitable zone in the same place for all planets in an SS?
No, it can vary with all the individual properties of a planet
How is the habitable zone of an SS dependent on the star?
Brighter stars have wider, further out HZs, while low mass stars have thinner, closer HZs
Can the HZ change locations over the life of a star?
Yes, usually a star increases in luminosity throughout its lifetime, therefore expanding the HZ
